Types of transistors

Because they are one of the most widely used components in the world of electronics, there are different types of transistors, each one is designed to be used mainly in one of its functions, either as a switch or as an amplifier. Although the same semiconductor materials (Material N and P) are used, the structure of each type changes somewhat in terms of material size or position. In some types you can change the name or the number of terminals.

Types of transistors

Junction transistors or UJT

This type is also known as a junction or UJT by the acronym in English ( U ni J unction T ransistor), in terms of its construction is totally different from the best known, since its internal structure is composed of only two semiconductor materials : an N-type bar where two bases are found and an embedded P-type material that acts as the emitter. The operation of this transistor is based on three regions called cutoff, saturation, and negative resistance (read more soon).

UJT transistor

Bipolar Transistors or BJT

Its abbreviations BJT come from «Bipolar Junction transistor», this is because the holes that are positive charges and the electrons as negative charges participate in the operating process. Within this type we can find the PNP and NPN transistors , despite having two different types, their operation is the same, they only have a small difference, and that the former are used for positive voltages and the latter for negative voltages. The BJT is controlled travez current and are the most common, because they are used in the analog electronic amplifiers and digital as switches. Read more about (operation, configurations, polarizations, etc)…

BJT transistor

Field Effect Transistors or FETs

These types of transistors are known as F ield E ffect T ransistor because they generate an electric field that is what controls the operation of the device. The FET are considered as unipolar transistors since depending on the type is the conduction that is achieved, if they are N-channel it conducts electrons and if they are P-channel it conducts holes. One of its main characteristics is that these components can behave as if they were resistors and capacitors giving the possibility of making circuits using pure FET transistors. (Next article to treat)

FET transistor

Within the field effect transistors we can find some variations such as:

  • JFET ( J unction F ield E ffect T ransistor)
  • IGFET ( I nsulated G ate F ield E ffect T ransistor)
  • MOSFET ( M etal O oxide S emiconductor F ield E ffect T ransistor)


Despite the fact that a phototransistor has only two terminals and a totally different appearance, the operation is practically the same as that of a normal transistor, since it is possible to regulate the collector current through the base, which in this case would be the encapsulation. Its operation depends directly on how much light reaches the base, since the more light it reaches the more current it generates. (Read more soon …)


HBT and HEMT transistor

These types of transistors are formed by a heterojunction , that is, they can be made up of a junction of two semiconductors of different material or a junction of a metal with a semiconductor. Within this type of junctions there are two different isotopes, which are when the conductivity of the two materials is the same and anisotypes that are the opposite, when the conductivity is different in each material.


The abbreviations of the HBT transistor are dated by H eterojunction B ipolar T ransistor, it is practically an improvement of the BJT transistors since it is capable of controlling very high frequency signals up to hundreds of GHz. They are mainly used in circuits where the response has to be fast as for example in radio frequency.


This transistor is of the field effect type and is known by different names, either as HEMT (High Electron Mobility Transistor), HFET or MODFET, its structure is formed by a PN heterojunction that uses materials such as gallium-aluminum arsenide (ALGaAs ) and gallium arsenide (GaAs). These are used because they have high electron mobility, high gain, and low noise levels. Its main applications are based on small low noise signal amplifiers, oscillators, and mixers that operate at frequencies up to 60 GHz.

HEMT transistor